Exposure to ionizing radiation can occur in many ways, both accidental and therapeutic. The most familiar exposure to radiation occurs when cancer patients undergo radiation therapy as part of their treatment.
Organs and body systems most sensitive to the effects of ionizing radiation include the skin, hematopoietic and lymphatic systems, gonads, lungs, nerve tissues and the GI tract. In the case of whole body radiation exposure, all organ systems will be exposed to the effects of ionizing radiation.
Radiation cell damage is mediated by one or more mechanisms. In particular, cell damage is caused by the ionization of various cellular molecular systems (the “direct hit” theory for lipids in various membranes, breakage of the DNA strands, and other targets), or by the formation of free “hot” radicals (e.g., superoxide or hydroxyl radicals) in sufficient quantities to begin chain reactions to form other reactive free radicals, which react with, damage and eventually kill the affected cells (the “indirect hit” theory).
The most radiosensitive organs include the rapidly dividing cells of the intestine, kidneys and bone marrow. Conditions that may develop from exposure to radiation include xerostomia, esophagitis, colitis, proctitis, pneumonitis, dermatitis, nephritis, myelitis, pericarditis and myocarditis, and life threatening infections secondary to compromise of the normal bone marrow function and lowering of the blood neutrophil and lymphocyte counts, among others.
Radiation therapy for cancer is a widely used regimen of treatment for many common types of cancer, and is often employed in combination with surgery and/or chemotherapy. Despite modern safety precautions and improved methods of directing radiation at the tumor so as not to damage healthy cells, radiation therapy still presents significant risks to the patient.
Mesna (sodium 2-mercaptoethene sulfonate) and dimesna (disodium 2,2′-dithiobis ethane sulfonate) are known therapeutic compounds that have heretofore demonstrated a wide variety of therapeutic uses. Both mesna and dimesna have been shown to be effective protective agents against certain specific types of toxicity associated with the administration of cytotoxic drugs used to treat patients for various types of cancer.
In particular, mesna has been used with some success in preventing or mitigating the toxic effects of cytotoxic agents such as ifosfamide, oxazaphosphorine, melphalan, cyclophosphamide, trofosfamide, sulfosfamide, chlorambucil, busulfan, triethylene thiophosphamide, triaziquone, and others, as disclosed in U.S. Pat. No. 4,220,660, issued Sep. 2, 1980.
The near absence of toxicity of dimesna further underscores the usefulness of this compound, as large doses can be given to a patient without increasing the risk of adverse effects from the protective agent itself.
Further, pharmacological profiles of each compound indicate that, if proper conditions are maintained, mesna and dimesna do not prematurely inactivate primary therapeutic drugs to a significant degree. Thus, neither compound will significantly reduce activity of the chemotherapeutic agent, and in many cases, act to potentiate the effect of the main drug on targeted cancer cells.
The structures of both mesna and dimesna are shown below as Formula A and Formula B, respectively.

As is well known, dimesna is a dimer of mesna, with the optimum conditions for oxidation occurring in the slightly basic (pH˜7.3), oxygen rich environment found in blood plasma. In mildly acidic, low oxygen conditions, in the presence of a reducing agent such as glutathione reductase, conditions prevalent in the kidneys, the primary constituent is mesna.
Mesna acts as a protective agent for a number of cytotoxic agents by substituting a nontoxic sulfhydryl moiety for a toxic TO hydroxy (or aquo) moiety. This action is particularly evidenced in the coadministration of mesna and oxazaphosphorine, and in the administration of dimesna along with cisplatin or carboplatin.
Mesna and dimesna, as well as some analogues of these compounds, have excellent toxicity profiles in mammalian species. However, it is clear from our earlier discoveries that dimesna has a much lower degree of toxicity relative to mesna; this lower degree of toxicity for dimesna imparts additional therapeutic value to this invention for radiation therapy since it is contemplated that chronic or high doses of dimesna will be needed in some circumstances in order to provide adequate prophylaxis for radiation toxicity as well as for treatment of acute or chronic radiation toxicity. In fact, dimesna has been administered intravenously to mice and dogs in doses higher than the accepted oral LD50 for common table salt (3750 mg/kg), with no adverse effects. Dimesna has also been administered to humans in doses exceeding 15 g/m2, with no major adverse effects.
Mesna, and other analogues with free thiol moieties, constitute the more physiologically active form of the two types of compounds described in this specification. These compounds manifest their activity by providing free thiol moieties for terminal substitution at locations where a terminal leaving group of appropriate configuration is located.
Dimesna and other disulfides can be activated intracellularly by glutathione reductase, a ubiquitous enzyme, thereby generating high concentrations of intracellular free thiols. These free thiols act to scavenge the radiation and other nucleophilic compounds often responsible for causing cell damage.
This profile is especially significant in explaining the success of dimesna in controlling and mitigating the toxic effects of platinum complex antitumor drugs. The mechanism for action in the case of cisplatin (cis-diammine dichloro platinum) is explained in U.S. Pat. No. 5,789,000, which is incorporated herein by reference.
Mesna, dimesna, and analogues of these compounds have been the subject of several prior pharmaceutical uses described in the literature and in prior patents, both in the United States and around the world. In addition to the cytotoxic agent protection uses, one or more of these compounds have proven effective, in vitro, against a multiplicity of biological targets, and have been effective, in vivo, in the treatment of sickle cell disease, chemical agent exposure, and other uses. Mesna, dimesna and analogues generally distribute well to the kidneys, intestine, bone marrow and extracellular space.
Mesna, dimesna, and analogues thereof are synthesized from commonly available starting materials, using acceptable routes well known in the art. One such method involves the two-step, single pot synthetic process for making dimesna and like compounds of the following formula:R1—S—R2;
wherein:                R1 is hydrogen, X-lower alkyl, or X-lower alkyl-R3;        R2 is -lower alkyl-R4;        R3 and R4 are each individually SO3M or PO3M2;        X is absent or X is sulfur; and        M is an alkali metal.        
The process essentially involves a two-step single pot synthetic process that results in the conversion of an alkenyl sulfonate salt or acid to the desired formula I compound. The process in the case of mesna is a single step process that converts the alkenyl sulfonate salt to mesna or a mesna derivative by reacting with an alkali metal sulfide or with hydrogen sulfide.
If the desired end product is dimesna or a dimesna analogue, a two-step single pot process is involved. Step 1 is as described above. Step 2 of the process is performed in the same reaction vessel as Step 1 without the need to purify or isolate the mesna formed during that step. Step 2 includes the introduction of oxygen gas into the vessel, along with an increase in pressure and temperature above ambient values, at least 20 pounds per square inch (psi) and at least 60° C. Dimesna or a derivative thereof is formed in essentially quantitative yield.
Other processes, well known and documented in the prior art, may be employed to make either mesna or dimesna, or derivatives and analogues thereof.